There is a helpful "LaTeX Guide" link below the Edit window to get you started. Note that you put double-$ delimiters at the start and end of each stand-alone line of LaTeX, and double-# delimiters at the start and end of in-line LaTeX that does not need to be on its own line.
Example of in-line LaTeX: ##v(t) = L \frac{di(t)}{dt}##
Example of stand-alone LaTeX:
$$v(t) = L \frac{di(t)}{dt}$$
Also, if you right-click on a LaTeX equation in a post, you get a pop-up menu to let you view the LaTeX source or view it in other formats.
LaTeX isn't supported in thread titles, so you can use simple text math in titles if you want.
Note also that PF uses a feature called "lazy LaTeX rendering" that speeds up page loads. When you first post your LaTeX in a thread, you will not see it rendered that first time. Just refresh your browser page to force it to be rendered, and then it should render whenever you come back to that page/thread in the future.
If you have trouble using the Preview feature to check your LaTeX, you can use a website such as
https://www.quicklatex.com/ or
https://latexeditor.lagrida.com/ to preview your LaTeX before you post it.